The present invention relates in general to the design and construction of cylinder heads for internal combustion engines. More specifically the present invention relates to modifications to the internal construction of a cylinder head and cylinder head casting in order to add stiffening and lower the deflections which the cylinder head would otherwise experience. The lower deflections result in lower total stresses in the cylinder head and cylinder head casting and this improves the durability of the cylinder head casting.
Cylinder heads of internal combustion engines commonly experience high stresses due to cylinder pressure and assembly loading. These loads often lead to high cycle fatigue cracks in the cylinder head casting. This in turn causes the cylinder head casting to be replaced with a new part, an event which results in a significant cost being incurred by the customer or by the manufacturer if the cylinder head is still under warranty, which is often the case.
There are a number of internal cavities which are created in a cylinder head which are essential to its intended functioning during the operation of the engine. These internal cavities include an upper water jacket, a lower water jacket, intake ports, and exhaust ports. These internal cavities are often highly stressed due to a combination of assembly loads and cylinder pressure loads. This combination of loads and the overall loading experienced by the cylinder head typically results in high tensile stresses in one or more of the fillets within the upper water jacket. While the lower water jacket fillets may also experience higher tensile stresses at load versus no load, the size of the corresponding water passageway does not create the same level of concern as that of the upper water jacket, nor does the specific location of the lower water jacket create the same level of concern.
The presence of higher tensile stresses in the fillets of the upper water jacket causes these fillets to become points of weakness and, with continued operation of the engine, these fillets will in time experience high cycle fatigue cracks. Once the high cycle fatigue cracks appear, the situation only becomes worse and ultimately the cylinder head casting must be replaced. While high cyclic loading and high tensile stresses, regardless of the cause, can in time lead to some mode of failure or at least performance deterioration, the issue is how quickly this occurs and the magnitude of the failure. In the case of a cylinder head, hundreds of thousands of miles are expected without any mode of failure that significantly detracts from engine performance. Obviously any substantial reduction in this expected duty cycle is unacceptable.
Even if a suitable minimum duty cycle, meeting the expectations of the manufacturer and purchasers, could be provided, an extended duty cycle for a cylinder head and cylinder head casting would still present an improvement in cylinder head design. With an extended duty cycle, the purchaser receives a better, more reliable cylinder head. The present invention is directed to this end result by incorporating gusset-like ribs in the upper water jacket to actually eliminate one or more of the fillets that are likely to experience (prematurely) high cycle fatigue cracks. By removing one or more of these fillets, there is less likelihood of a crack initiating, resulting in a more durable cylinder head casting and, in turn, an improved cylinder head.